As is well known, in water softening ionic exchange resins are used, which attract with their negative ions the positive calcium and magnesium ions suspended in the water. Such resins, normally constituted by small pearls, are housed in a containment compartment provided with a valve for controlling the water. The control valve determines the introduction of a predefined quantity of hard water and the subsequent outflow of the softened water.
In detail, appropriate supply conduits associated to the valve direct the water through the resins in such a way that the resins act by retaining the calcium and magnesium contained in the water.
Normally, the resins must be periodically regenerated to restore the value of sodium originally present thereon and remove the minerals taken from the water, which cause its hardness.
Said step of regenerating the resins consists of the introduction of a brine into the containment compartment.
In particular, to remove any impurities in suspension, the spherical resins are previously washed with counter flowing water. At this point, the brine is supplied by aspiration and fed into the containment compartment in which the resins are housed. The brine is aspirated by effect of the vacuum created by the passage of actuating water appropriately fed by the valve.
At the end of the operation of supplying the brine, a further rinse with water alone is conducted, to remove any residues in suspensions due to the passage of the brine. This wash is generally conducted with equal flow, i.e. feeding water into the containment compartment with a flow having the same direction as the direction of feeding of the water to be softened.
The regeneration method described above is conducted in devices for softening water of two types, commonly known by the terms “up flow” and “down flow”. Such devices are differentiated by the direction of flow of the brine which in one case is directed from the lower portion of the containment compartment upwards, and in the other case is directed from the upper portion of the containment compartment downwards.
However, in both these devices, the resin regeneration method has some drawbacks.
A first drawback is linked to the poor efficiency of regeneration of the resins, which in contact with the brine doe not fully exploit the ionic exchange capacity.
Moreover, it should be noted that the resin regeneration steps entail a high consumption of salt and water, used to aspirate the brine and to wash the resins.
Lastly, a further drawback is that the first step of counter-flow washing causes a turbulence within the containment compartment which creates compacted resin blocks with the consequent formation of preferential passages of the water and of the brine. In this situation, the water and the brine are arranged in non uniform fashion among the resins.